1. Field of the Invention
The present invention relates to pressure measurement in a pressurized fluidized bed and more particularly to maintaining the integrity of a pressure measurement tap and keeping it clear of particulate matter.
2. Description of the Related Art
It has been a continuing problem to take a pressure measurement from a pressurized fluidized bed because particulate matter from the fluidized bed tends to become clogged in the pressure measurement tap. One method used to prevent the flow of particulate into the tap is to use a pressure measurement tap which has an opening for a purge air flow. The purge air flow is opposite the flow of particulate matter and forces the particulate back into the pressurized fluidized bed. The air flow has to be rapid enough to prevent the particulate matter from clogging the pipe but slow enough not to effect the pressure reading being taken upstream of the inserted pipe.
U.S. Pat. No. 4,552,529 discloses one variation of this method. In this patent the pressure tap is off of a "T" connection with the purge air constantly flowing past the pressure measurement point. This produces high fluctuations between readings and also has a small range of pressure differentials in which effective readings may be taken.
U.S. Pat. No. 5,241,863 discloses a device for isolating the pressure measurement gauge from the particulate air that might be flowing in through the measurement point tube. The particulate air is isolated from the pressure measurement tube by a baffle in a chamber. It discloses the use of a purge air inlet located on the pressure measurement gauge side of the baffle. Its purpose is to keep the particulate matter from forming and building up in the measurement tube or flowing past the baffle. The measurement gauge opening is not isolated from the purge air in this design.
U.S. Pat. No. 4,651,575 teaches the use of a venturi tube to speed the gas or fluid through the measurement point to keep the measurement tube clean. In addition, this patent discloses two points where purge air can be vented into the venturi tube to also aid in the cleaning effect.
In U.S. Pat. No. 3,295,374, a device using purge air flowing past the point of measurement to keep the measurement point clean of particles is disclosed. The device has a control mechanism for controlling the purge air flow.